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G8MNY > TECH 12.07.03 23:16l 49 Lines 2337 Bytes #999 (0) @ WW
BID : 5392_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: Making a Phasing Harness
Path: DB0FHN<DB0RGB<OK0PPL<RZ6HXA<HA3PG<IK1ZNW<EA7URC<GB7CRV<GB7CIP
Sent: 030712/2026Z @:GB7CIP.#32.GBR.EU #:5392 [Caterham] $:5392_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY
Calculate 1/4 wave lengths of 75ê coax using the coax's velocity factor & the
wave length for your frequency of interest. None of this is too critical unless
above 1GHz, where cable Z change if you bend them & cutting to length is more
of an art, so the use of a solid power splitter is more common.
Decide which harness design you want:-
Join Tee == to aerial tee ========#== to aerial
50ê =======<ðððððððð[ 2x 50ê OR 50ê =======[ 2x75ê 2x 50ê
37ê == to aerial ========#== to aerial
(2x75ê)
eg both matching lines in a single feed plug (or socket) & an aerial plug (or
socket) with a aerial T connector. Or use the matching lines as the T with 3
plugs (or sockets). The latter is mechanically less strong, & waterproofing
may be more difficult. Alternatively you could splice in the matching sections,
but again waterproofing can be a problem.
Use good quality 75ê cable with heavy braid. You should find that 2 coaxes can
be made to fit N connectors with some difficulty. Use silicon rubber or grease
to seal/fill connectors once tested.
Testing can be done with a sensitive SWR meter a 1W rig & 2x small 47ê
resistors (with minimum leads) mounted one the ends of the lines to simulate
the 2 aerials. This should prove the cut lengths are OK before you terminate
the aerial ends.
The Aerials must be identical types (no early/later multibeam type mix). And
mounted so that the connections feed the same side of the driven aerial element
to be in phase. If the aerials are mirror images (one up side down) and the
element cannot be rotated, then add 1/2 wave length (x Velocity factor) to one
of the 50ê aerial feeders. The two aerial feed coaxes between the splitter &
aerials must be identical lengths & type.
Aerial spacing, is variable, the manufacturers data may help, but a good guide
is about half the boom length. This rule of thumb, makes sure the aerials
capture areas do not overlap. Closer stacking/baying, gives variable results as
all the aerial elements will couple, & this will result in a different polar
diagram/gains than optimum. But closely mounted aerials with high gains are
possible, if difficult to get the distance right!
/QSL
73 De John, G8MNY @ GB7CIP
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